Petroleum is a limited, natural resource found in the Earth in liquid, gaseous, or solid forms. Petroleum is primarily composed of hydrocarbons, which are comprised mainly of carbon and hydrogen. It also contains significant amounts of other elements, such as, nitrogen, oxygen, or sulfur, in different forms.
Petroleum is a valuable resource, but petroleum products are developed at considerable costs, both financial and environmental. First, sources of petroleum must be discovered. Petroleum exploration is an expensive and risky venture. The cost of exploring deep water wells can exceed $100 million. Moreover, there is no guarantee that these wells will contain petroleum. It is estimated that only 40% of drilled wells lead to productive wells generating commercial hydrocarbons. In addition to the economic cost, petroleum exploration carries a high environmental cost. For example, offshore exploration disturbs the surrounding marine environments.
After a productive well is discovered, the petroleum must be extracted from the Earth at great expense. During primary recovery, the natural pressure underground is sufficient to extract about 20% of the petroleum in the well. As this natural pressure falls, secondary recovery methods are employed, if economical. Generally, secondary recovery involves increasing the well's pressure by, for example, water injection, natural gas injection, or gas lift. Using secondary recovery methods, an additional 5% to 15% of petroleum is recovered. Once secondary recovery methods are exhausted, tertiary recovery methods can be used, if economical. Tertiary methods involve reducing the viscosity of the petroleum to make it easier to extract. Using tertiary recovery methods, an additional 5% to 15% of petroleum is recovered. Hence, even under the best circumstances, only 50% of the petroleum in a well can be extracted. Petroleum extraction also carries an environmental cost. For example, petroleum extraction can result in large seepages of petroleum rising to the surface. Moreover, offshore drilling involves dredging the seabed which disrupts or destroys the surrounding marine environment.
Since petroleum deposits are not found uniformly throughout the Earth, petroleum must be transported over great distances from petroleum producing regions to petroleum consuming regions. In addition to the shipping costs, there is also the environmental risk of devastating oil spills.
In its natural form, crude petroleum extracted from the Earth has few commercial uses. It is a mixture of hydrocarbons (e.g., paraffins (or alkanes), olefins (or alkenes), alkynes, napthenes (or cylcoalkanes), aliphatic compounds, aromatic compounds, etc.) of varying length and complexity. In addition, crude petroleum contains other organic compounds (e.g., organic compounds containing nitrogen, oxygen, sulfur, etc.) and impurities (e.g., sulfur, salt, acid, metals, etc.).
Hence, crude petroleum must be refined and purified before it can be used commercially. Due to its high energy density and its easy transportability, most petroleum is refined into fuels, such as transportation fuels (e.g., gasoline, diesel, aviation fuel, etc.), heating oil, liquefied petroleum gas, etc.
Crude petroleum is also a primary source of raw materials for producing petrochemicals. The two main classes of raw materials derived from petroleum are short chain olefins (e.g., ethylene and propylene) and aromatics (e.g., benzene and xylene isomers). These raw materials are derived from longer chain hydrocarbons in crude petroleum by cracking it at considerable expense using a variety of methods, such as catalytic cracking, steam cracking, or catalytic reforming. These raw materials are used to make petrochemicals, which cannot be directly refined from crude petroleum, such as monomers, solvents, detergents, or adhesives.
One example of a raw material derived from crude petroleum is ethylene. Ethylene is used to produce petrochemicals, such as polyethylene, ethanol, ethylene oxide, ethylene glycol, polyester, glycol ether, ethoxylate, vinyl acetate, 1,2-dichloroethane, trichloroethylene, tetrachloroethylene, vinyl chloride, and polyvinyl chloride. An additional example of a raw material is propylene, which is used to produce isopropyl alcohol, acrylonitrile, polypropylene, propylene oxide, propylene glycol, glycol ethers, butylene, isobutylene, 1,3-butadiene, synthetic elastomers, polyolefins, alpha-olefins, fatty alcohols, acrylic acid, acrylic polymers, allyl chloride, epichlorohydrin, and epoxy resins.
These petrochemicals can then be used to make specialty chemicals, such as plastics, resins, fibers, elastomers, pharmaceuticals, lubricants, or gels. Particular specialty chemicals that can be produced from petrochemical raw materials are fatty acids, hydrocarbons (e.g., long chain, branched chain, saturated, unsaturated, etc.), fatty alcohols, esters, fatty aldehydes, ketones, lubricants, etc.
Aldehydes are used to produce many specialty chemicals. For example, aldehydes are used to produce polymers, resins (e.g., Bakelite), dyes, flavorings, plasticizers, perfumes, pharmaceuticals, and other chemicals. Some are used as solvents, preservatives, or disinfectants. Some natural and synthetic compounds, such as vitamins and hormones, are aldehydes. In addition, many sugars contain aldehyde groups.
Obtaining these specialty chemicals from crude petroleum requires a significant financial investment as well as a great deal of energy. It is also an inefficient process because frequently the long chain hydrocarbons in crude petroleum are cracked to produce smaller monomers. These monomers are then used as the raw material to manufacture the more complex specialty chemicals.
In addition to the problems with exploring, extracting, transporting, and refining petroleum, petroleum is a limited and dwindling resource. One estimate of world petroleum consumption is 30 billion barrels per year. By some estimates, it is predicted that at current production levels, the world's petroleum reserves could be depleted before the year 2050.
Finally, the burning of petroleum based fuels releases greenhouse gases (e.g., carbon dioxide) and other forms of air pollution (e.g., carbon monoxide, sulfur dioxide, etc.). As the world's demand for fuel increases, the emission of greenhouse gases and other forms of air pollution also increases. The accumulation of greenhouse gases in the atmosphere can lead to an increase global warming. Hence, in addition to damaging the environment locally (e.g., oil spills, dredging of marine environments, etc.), burning petroleum also damages the environment globally.
Due to the inherent challenges posed by petroleum, there is a need for a renewable petroleum source that does not need to be explored, extracted, transported over long distances, or substantially refined like petroleum. There is also a need for a renewable petroleum source which can be produced economically without creating the type of environmental damage produced by the petroleum industry and the burning of petroleum based fuels. For similar reasons, there is also a need for a renewable source of chemicals which are typically derived from petroleum.
One method of producing renewable petroleum is by engineering microorganisms to produce renewable petroleum products. Some microorganisms have a natural ability to produce chemicals. For example, yeast has been used for centuries to produce ethanol (e.g., beer, wine, etc.). In recent years, through the development of advanced biotechnologies, it is possible to metabolically engineer an organism to produce bioproducts that were never previously produced. Products, such as chemicals, derived from these cellular activities are known as bioproducts. Fuels produced these cellular activities are known as biofuels. Biofuels are a renewable alternative fuel to petroleum based fuels. Biofuels can be substituted for any petroleum based fuel (e.g., gasoline, diesel, aviation fuel, heating oil, etc.). Biofuels can be derived from renewable sources, such as plant matter, animal matter, or even waste products. These renewable sources are collectively known as biomass. One advantage of biofuels over petroleum based fuels is that they do not require expensive and risky exploration or extraction. In addition, biofuels can be locally produced. Hence, they do not require transportation over long distances. Moreover, biofuels can be made directly without the need for expensive and energy intensive refining as is needed with refining crude petroleum. In other circumstances, the biofuel may require a limited and cost-effective level of refining. Furthermore, the use of biofuels improves the environment by reducing the amount of environmentally harmful emissions (e.g., green house gases, air pollution, etc.) released during combustion. For example, biofuels maintain a balanced carbon cycle because biofuels are produced from biomass, a renewable, natural resource. While the burning of biofuels will release carbon (e.g., as carbon dioxide), this carbon will be recycled during the production of biomass (e.g., the cultivation of crops), thereby balancing the carbon cycle unlike petroleum based fuels.
For similar reasons, biologically derived chemicals offer the same advantages as biofuels over petroleum based fuels. Biologically derived chemicals are a renewable alternative to petrochemicals. Biologically derived chemicals, such as hydrocarbons (e.g., alkanes, alkenes, or alkynes), fatty alcohols, esters, fatty acids, fatty aldehydes, and ketones are superior to petrochemicals because they are produced directly without extensive refining. Unlike petrochemicals, biologically derived chemicals do not need to be refined like crude petroleum to recover raw materials which must then be further processed to make more complex petrochemicals. Biologically derived chemicals are directly converted from biomass to the desired chemical product.